Process of metal treatment



Jan. 8, 1935. c. F. LAuENsTElN PROCESS OF METAL TREATMENT vb' v... ....i. ...2.

Filed Feb.

C. F. LAUENSTEIN PROCESS oF METAL TREATMENT Jan. 8, 1935.

Filed Feb. 1'7

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PROCESS OF METAL TREATMENT I Filed Feb. 1v, 195o s sheets-sheet s Jzvenfa? l Parente Jan. s, i935 UNITED STATES PROCESS F METAL TREATLIENT Carl F. Laue to Link tion of Illinois nstein, Indianapolis, 1nd., assignor -Belt Company, Chicago,

lll., a. corpora- Application February 17, 1930, Serial No. 428,952

12Claims.

y'Ihis invention relates to the problem of annealing a ferrous alloy and has for one object to provide a means for accomplishing the complete cycle of annealing rapidly. Other objects will appear from the time to time in the specification and claims.

The invention 'may be applied to the manufacture of malleable castings and it will be described herewith as so applied. The iron alloy most generally used for castings which are to be malleabilized is known usually as white iron and it consists mainly of iron and carbon. It may also contain, among other things, silicon, manganese, sulphur,'phosphorus and relatively small amounts of impurities. After the casting operation is completed all, or practically all, of the carbon is in combination with the iron in the form of iron carbides. The general object of the annealing operation is to throw the carbon out of combination with the iron so that after the annealing the carbon is in the form of globules or crystals, separate from and interspersed between the crystals of the ferrite.

The following drawings illustrate various stages in the manufacture of the metal which forms the subj ect of the present invention. They are drawings made in reproduction of microphotographs.

Fig. l illustrates white cast iron;

. 2 is a similar view showing the iron after it has been heated for four hours at 1650 F.;

Fig. 3 is the iron after it has been heated for four hours at 1650" F. and four hcurs at 1850 F.;

Fig. 4 is iron after it has been heated four hours at 1650" F. and 4 hours at 18507 F., and cooled to a point below the critical temperature, approximately 1375" F.;

Fig. 5 is Vthe finished product after it has rev ceived the two beatings above mentioned and 40- after it has been cooled first to approximately 1400 F., then at a controlled rate of speed to 1200o F. and subsequently cooled to room temperature.

In Fig. 1 the relatively white areas A are cementite and the gray or relatively dark areas B are an iron carbide in the form of pearlite, sorbite or troostite, depending on the rate at which the casting was cooled.

In Fig. 2 the,white areas A have decreased. 50 They still represent cementite. 'I'he gray areas still indicate iron carbide and certain darker areas C have appeared. 'I'hese are graphitic carbon.

In Fig. 3 the black areas C have increased in size and the white has disappeared. 'I'he black areasV represent, as before, carbon; the gray areas B represent iron carbide.

In Fig. 4 the black areas C of carbon have in- .creased somewhat, the gray area represents iron carbides and the white area D represents ferrite from which all of the carbon has been removed.

Fig 5, representing as it does the finished product, shows widely diversified and relatively small black areas C of carbon and the remainder of the body of the metal is made up essentially of white areas D which are ferrite grains.

In the past the malleabilizing process has been slow. 'I'he iron has been normally heated to approximately 1650 F. 'Ihis does not throw all of the carbon out of combination with the ferrite. It thus does not remove all of the iron carbide. The iron is raised to the heat mentioned and held there sufficiently long to permit f whatever chemical change which can take place to take place. The casting is then cooled to about the critical temperature, somewhere between 1350 F. and 1375 F. As a result of this cooling a further quantity of the carbon is thrown out of combination. However, an appreciable residue of carbon still remains in combination. The usual method of getting this nal residue out of combination is to cool extremely slowly through the critical range, the rate of cooling being about 5" F. perl hour and this nal stage frequently requires as much as 48 hours.

Experiments have shown that by increasing the temperature of the initial heating above 1650 F. the carbon can be thrown out very much more rapidly and the process greatly shortened and, within certain limits, the higher the heat the greater the rapidity with which the initial or partial breakingdown of the iron carbide may be accomplished, for example, the time required when the metal is heated to approximately 1850 F. is something less than one-third that required when it is heated to only 1750 F. It was found, however, that the carbon, when thrown off as the result of this high heat, when heated to this temperature rapidly, takes on a peculiar form. Instead of being in the form of a relatively large number of relatively small globules'or balls, carbon is found in a relatively small number of relatively large irregularly shaped, angularly formed bodies with` points running out from the main body and penetrating between the ferrite grains. Such a carbon formation reduces the strength and ductility of the m'shed product. Probably this is caused by the fact that when the carbon is precipitated at such a high rate of speed, it cannot form small areas but forms rather` into a relatively few large, irregularly shaped areas or bodies. It is one of the objects of this invention to avoid the defect just mentioned and to secure the benefit of the rapid speed by the use of the high temperatures while causing the carbon, when precipitated out, to take the better form of a relatively larger number of rounder or more nearly ball shaped areas or bodies.

The solution ofthe diiliculty above indicated was found by heating the metal preferably at a rapid rate, rst to approximately 1650 F. and holding it at that temperature for a relatively short period, in one example, for four hours; subsequently the metal was heated to 1850 F. approximately, and was held at that temperature for a short period, for example, about four hours; it was then cooled to about 1400 F. and held at that temperature for the time necessary to allow the temperature to equalize itself throughout all the material being treated, in one example this was approximately one hour; after that it was cooled to approximately 1200 F. at a controlled rate which may be about 8 F. per hour. It was foimd that by this heat treatment a satisfactory malleable iron was formed and that the carbon appeared in a large number of bodies and that these were of a satisfactory form and shape. The time required under this method for the complete cycle of annealing, is in the neighborhood of 37 hours as compared to the usual seven or eight days for a complete annealing cycle by the method now generally practiced in the art.

It is believed that this method, which has proved in practice to be successful and, as indicated, greatly reduces the time required for the complete annealing cycle, operates in the following steps: 'Ihe metal is rst heated to approximately 1650 F. and held at that temperature about four hours. This heating, while not suilicient to throw out of combination all of the carbon, which can be thrown out at that temperature, is sumcientto throw out some of it and there is thus formed a large number of relatively small carbon nuclei. The metal is then heated to a higher temperature, approximately 1850 F. The remaining carbon is rapidly thrown out of combination and, due to the fact that a large number of carbon nuclei has already been formed at the lower temperature, this additional carbon now thrown out at the higher temperature goes into the nuclei already formed and the nal result is that the metal embodies a large number of small carbon bodies of satisfactory form and shape, rather than the very few large bodies formed where the rst heating is carried out at the extremely high heat.

I claim:

1. The process of heat treating white cast iron to precipitate the carbon which includes heating to `approximately 1650 F., holding at that temperature for a time suflcient partially to precipitate the carbon and to cause it to form into a relatively large number of relatively small, widely dispersed carbon nuclei, heating to approximately 1850 F., holding at that temperature for a time suilicient to complete the precipitation of the remaining carbon into the nuclei so formed, cooling to approximately 1400" F. and holding at that temperature for a time.

2. The process of heat treating white cast iron to precipitate the carbon which includes heating to approximately 1650 F.. holding at that temperature for a time sulcient partially` to precipitate the carbon and to use it t0 Qllll into perature of 1400 F.

a relatively large number of relatively small, widely dispersed carbon nuclei, heating to approximately 1850 F., holding it at that temperature for a time sufficient to complete the precipitation of the remaining carbon into the nuclei so formed. cooling to approximately 1400 F., holding at that temperature for a time, and subsequently cooling to approximately 1200 F. at a controlled rate of cooling.

3. The process of heat treating white cast iron to precipitate the carbon which includes heating to approximately 1650 F., hlding at that temperature for a time suilicient partially to precipitate the carbon and to cause it to form into a relatively large number of relatively small, widely dispersed carbon nuclei, heating to approximately 1850 F., holding it at that temperature yfor a time suillcient to complete the precipitation of the remaining carbon into the nuclei so formed, cooling to approximately 1400 F., holding at that temperature for a time, and subsequently cooling to approximately 1200 F., at a rate of approximately 8 F. per hour.

4. 'I'he process of heat treating white cast iron t-o precipitate the carbon which includes heating to approximately 1650 F., holding at that temperature approximately four hours, heating it to approximately 1850 F., holding at that temperature for a substantially equal period, cooling to approximately 1400 F., and holding at that temperature for a less period.

5. 'Ihe process of heat treating white cast iron to precipitate the carbon which includes heating to approximately 1650 F., holding at that temperature approximately four hours, heating to approximately 1850 F., holding at that temperature for a substantially equal period, cooling to approximately 1400 F. and holding at the temperature of 1400" F. for approximately one hour.

6. The process of heat treating white cast iron to precipitatethe carbon which includes heating to approximately'l650" F., holding at that temperature approximately four hours, heating it to approximately 1850 F., holding at that temperature for a substantially equal period, cooling to approximately 1400 F., holding at that temperature for a less period, and cooling from said last mentioned temperature at a controlled rate of cooling.

'1. The process of heat treating white cast iron to precipitate the carbon which includes heating to approximately 1650 F., holding at that temperature approximately four hours, heating it to approximately 1850 F., holding at that temperature for a substantially equal period, cooling to approximately 1400 F. and holding at the temfor approximately one hour, and cooling from said last mentioned temperature Vat a controlled rate of cooling.

8. The process of heat treating white cast iron to precipitate the carbon which includes heating to approximately 1650 F., holding at that temperature approximately four hours, heating it to approximately 1850 F., holding at that temperature for a substantially equal period, cooling to approximately 1400 F. and holding at that temperature for a less period, and cooling from said last mentioned temperature at approximately 8 F. per hour until a temperature of approximately 1200 F. is reached.

9. The process of heat treating white cast iron to precipitate the carbon which includes heating to approximately 1650 F., holding at that temperature approximately four hours, heating it to approximately 1850 F., holding at that temperato approximately 1650 F., holding at that temperature approximately four hours, heating to approximately 1850 F.,lholding at that temperature for a substantially equal period, cooling rapidly to approximately 1400 F., and holding at "that temperature for a lessperiod, cooling from said last mentioned temperature at`approximately 8 F. per hour until a temperature of approximately11200 F. is reached and subsequently cooling toroom temperature atan uncontrolled rate of 1l. .The method o! heat treating white cast iron to precipitate the carbon, which includes heatingv the metal to and holding it at a temperature sufcient to precipitate some of the carbon relatively slowly to form a relatively large number of relatively small carbon nuclei and subsequently heating the metal to and holding it at a higher temperature to precipitate substantially all of the remaining available carbon.

12. The method of producing `malleable cast iron which comprises the steps of heating white cast iron to a temperature of approximately 1650 F., holding the casting at that temperature for a few hours, heating the casting to a temperature of approximately 1850 F., holding it at that temperature for a few hours, cooling the casting,

to a temperature of approximately 1400 F., hold- `ingy it at that temperature for 'a few hours, and

then further cooling the casting.

CARL F. LAUENSTEKIN. 2o 

